The processors used in such control units, e.g., engine control units, pump control units, brake control units, etc., are usually supplied with an external clock signal of an oscillator in the form of a quartz oscillator. The accuracy with which its clock frequency is adjustable has a direct influence on the computing accuracy of the respective processor. A device for supplying a clock signal for the processor of a control unit is described in German Patent Application No. DE 197 22 114, for example.
In the frequency interface transmission of measured values from a sensor to a control unit, the information regarding a measured quantity to be transmitted is contained in the period of the digital signals transmitted. Tolerance investigations here have shown that the oscillators which act for the sensor, which is used as the transmitter, and the control unit, which is used as the receiver, are to be taken into account in adjusting and/or estimating the system tolerance. For this reason, attempts have been made to use oscillators having a high precision, which has traditionally resulted in the use of quartz oscillators.
However, the use of quartz oscillators is associated with high costs, so an attempt is made as part of the present invention to avoid, if possible, the cost-intensive use of quartz oscillators in conjunction with the applications indicated above.